The interesting observation that A/He and C57BL/6 mice respond oppositely with respect to antibody production and delayed hypersensitivity to human gamma-globulin provides a useful model to study the regulation of these immunologic functions. A/He mice are high responders with respect to antibody production and make a poor delayed hypersensitivity response, while C57BL/6 mice make a good delayed hypersensitivity response and a poor antibody response. The proposed studies are directed toward determining the regulatory function of T suppressor cells in in vitro T-cell antigen-induced proliferation, T helper cell function in antibody synthesis and delayed hypersensitivity in vivo. Immunologic pertubations such as cyclophosphamide and antigen pretreatment will be utilized to study the mechanism whereby suppressor cells and/or circulating antibody regulate cellular and humoral immunnity.